It’s not really something they bring up, because they both get it.
The bunker is just… big. Bigger than anything they’ve ever had. Sam and Dean’s rooms are only a hallway apart, but it’s been too long, they both guess, of Sam and Dean’s beds being only a few feet apart, whether that’s the space separating two queens at a motel or just the distance between Baby’s front and back seats.
If relative safety was measured in distance from brother to brother, then for years they’ve felt safest asleep. They could sense each other in the dark; sight, sound, smell, taste, touch, you.
Without it was liveable, but endlessly uncomfortable. So the night Dean awoke from not-quite-sleep to Sam’s silhouette leaned against the doorframe, he just grunted in acknowledgement and moved to one side of the bed, pulling the covers back on the other.
When Sam’s weight settled beside him, Dean resisted the urge to sigh in relief. This was better. This made sense.
Sam was gone when he woke up, but there was an impression in the memory foam that was roughly Sam-sized, still warm from when he rose with the sun hours ago.
Neither mentioned anything, but the next night, when Dean knocked on the door to Sam’s room, Sam let him in. And when he woke at sunrise, he took one last look at his older brother in his bed and let it make him feel secure before going for his run.
Neither mentioned anything, but it came to be that whoever went to bed first, the other followed. Even when they fought, because even angry they couldn’t deny each other this.
The first time Sam jolted awake from a nightmare, Dean sensed it and woke seconds later, one hand flying to his brother’s face, his shoulder, the other curling its fingers around the .45 under his pillow.
When they locked eyes, Sam shook his head, no danger, and Dean paused, then nodded, relaxed again.
Sam shifted, but before he could turn, Dean caught his hand and pushed his fingers through Sam’s.
Dean’s eyes were already closed when Sam looked, so he squeezed their palms tight together, then released and shifted forward. Towards him.
And another night, when it was evidently Dean’s turn to have a nightmare, and he woke only to find himself wrapped in Sam’s arms, his baby brother’s face just millimeters from his, oh, it felt right.
“I’m here, Dean. I’m here. I’m here.”
In the morning he wasn’t, but that was fine, because they both get it.
In the morning when Sam wakes, or on the rare occasion that Dean wakes first, the indentation of one brother in the memory foam isn’t separated from the other’s. Daylight comes with a literal empty space where he should be.
In the morning, they’re both a little grumpy.
It’s worst on happy nights. Finished hunts and hard-earned rest, they learn, make them eager for each other’s touch. They smile tiredly as Dean runs fingers through Sam’s hair, Sam rubs circles at Dean’s waist, Dean noses into Sam’s neck. Constantly close enough to share breath, always, always, until they do.
Sam could easily plead temporary insanity; anyone so close to his big brother’s soft mouth could go a little crazy. Hell, Sam’s seen it happen himself.
He’s just never been the one, and he pulls away quickly, belatedly murmurs “Can I?”, and, thank God or whoever the fuck’s paying attention these days, Dean just smashes their lips back together.
Sam grunts just from relief but Dean pushes his tongue into his brother’s mouth and turns the sound into a moan, and it’s forceful but unhurried, pacifying. They fall asleep that way.
When Sam rises with the sun and finds his fingers clutched in Dean’s, he smiles to himself. Kisses the back of Dean’s knuckles, then his shoulder, then hums in pleased surprise at the kiss back when he reaches Dean’s lips.
“Sorry. Didn’t mean to wake you.”
“Hmm. Don’t look very sorry.”
His little brother gives him this fiendish grin, and his eyes narrow a little. “You’re right. I’m not.”
Then Sam’s weight settles over Dean’s hips and Dean’s whining into his mouth, thinking, damn, Sammy.